Waveguide slot radiators, utilized as antennas and the like, are relatively well known in the art. Typically, the narrow wall true transverse waveguide slots have been little used as practical radiating elements. This is possibly because the excitation methods described in the literature are physically unwieldly in the smaller waveguide sizes such as C, X, and KU bands. In the dominate waveguide mode transverse narrow wall waveguide slots are located in a portion of the waveguide wall in the neighborhood of which there is substantially no component of the oscillating electric field perpendicular to the waveguide wall and the electric field approaches zero toward such wall of the waveguide. Therefore, no radiation takes place without inserting a suitable probe into the guide adjacent to the slot to introduce asymmetry in the field and current distributions for excitation of a field across the slot. Such probes have typically been bent probes, such as disclosed in U.S. Pat. No. 2,574,433, issued Nov. 6, 1951, and entitled "System For Directional Interchange of Energy Between Waveguides and Free Space", or a loop generally as disclosed in U.S. Pat. No. 3,176,300, issued Mar. 30, 1965, and entitled "Adjustable Slotted Waveguide Radiator With Coupling Element".
The loop or bent probe types of implementation are far too critical in terms of physical tolerances for stable electrical parameters. However, with waveguide sizes of larger dimension such as WR-975 (i.e. 5.125 inches by 10.0 inches), the use of the bent probe or loop excited narrow wall edge slots become feasible. Investigation of the bent probe reveals that it has very limited capability in the amount of coupled excitation it can provide to a true narrow wall transverse edge slot. The usefulness of the slot excited in this mannner is thus limited. Greater coupling can be achieved by using the loop arrangement, but this geometry has the disadvantages of unsuitable narrow band impedance characteristics and very poor mechanical integrity.